With the advancement of technology, and the need for instantaneous information, the ability to transfer digital information from one location to another, such as from a central office (CO) to a customer premise (CP), has become more and more important.
A digital subscriber line (DSL) communication system is but one example of a number of communication systems that may simultaneously transmit and receive digital data between two locations. In a DSL communication system, data is transmitted from a CO to a CP via a transmission line, such as a two-wire twisted pair, and is transmitted from the CP to the CO as well, either simultaneously or in different communication sessions. The same transmission line might be utilized for data transfers by both sites or the transmission to and from the CO might occur on two separate lines. Specifically, FIG. 1 illustrates communication between a central office (CO) 10 and a customer premise (CP) 20 by way of twisted-pair telephone line 30. While the CP 20 may be a single dwelling residence, a small business, or other entity, it is generally characterized as having plain old telephone system (POTS) equipment, such as a telephone 22, a public switched telephone network (PSTN) modem 25, a facsimile machine (not shown), etc. The CP 20 may also include an DSL communication device, such as a DSL modem 23 that may permit a computer 24 to communicate with one or more remote networks via the CO 10. Often when a DSL service is provided, a POTS filter 21 is interposed between the POTS equipment such as the telephone 22 and the twisted-pair telephone line 30. As is known, the POTS filter 21 includes a low-pass filter having a cut-off frequency of approximately 4 kilohertz to 10 kilohertz, in order to filter high frequency transmissions from the DSL modem 23 and to protect the POTS equipment.
At the CO 10, additional circuitry is provided. Generally, a line card 18 containing line interface circuitry is provided for electrically coupling a data transmission to the twisted-pair telephone line 30. In fact, multiple line cards 14, 18 may be provided (two shown for simplicity of installation) to serve a plurality of local loops. In the same way, additional circuit cards are typically provided at the CO 10 to handle different types of services. For example, an integrated services digital network (ISDN) interface card 16, a digital loop carrier line card 19, and other circuit cards supporting similar and other communication services, may be provided.
A digital switch 12 is also provided at the CO 10 and is configured to communicate with each of the various line cards 14, 16, 18, and 19. On the outgoing side of the CO (i.e., the side opposite the various local loops), a plurality of trunk cards 11, 13, and 15 are typically provided. For example, an analog trunk card 11, a digital trunk card 13, and an optical trunk card 15 are illustrated in FIG. 1. Typically, these circuit cards have outgoing lines that support numerous multiplexed DSL service signal transmissions.
Asymmetric DSL (ADSL) is an important variation of the basic DSL. ADSL gets its name from its inherent asymmetry between the various data rates. The upstream data rate (i.e., the data from the CP 20 to the CO 10) is a factor of 10 smaller than the associated downstream data rate (i.e., the data from the CO 10 to the CP 20). The asymmetry of ADSL suits transmission control protocol/Internet protocol (TCP/IP) traffic quite well as it matches the expected upstream and downstream data rates associated with Internet technologies, making ADSL the DSL variation of choice for inexpensive high-speed Internet access. ADSL permits simultaneous POTS operation along the same twisted-pair telephone line 30, thereby allowing DSL service providers easy access to potential customers already connected to the PSTN. In addition to the asymmetry of the upstream and downstream data paths, ADSL uses rate adaptation techniques to select an optimum rate based on individual twisted-pair telephone line 30 conditions.
With ADSL transceivers, the maximum usable data rate may be determined by a number of factors. A first factor, the transceiver technology, may comprise the digital encoding and modulation scheme of the underlying ADSL communications standard, as well as, amplifier efficiency, and noise immunity associated with the hardware used to realize the DSL transceiver. A second factor may comprise the quality and distance of the twisted-pair telephone line 30 comprising a local loop used to provide a data transmission medium between the ADSL transceiver and an associated CO-ADSL transceiver that may be provided on the line card 18. A third factor may comprise the relative strength of local radio-frequency transmissions that may interfere with the DSL frequency range (not shown). With rate adaptive DSL communications systems, such as ADSL, slower data rates can be traded in exchange for increased distances between COs 10 and remote CPs 20.
In order to achieve higher data rates with a fixed distance or with a given non-rate adaptive DSL transceiver technology, two or more DSL lines may be combined. By way of example, high-speed DSL (HDSL) technology uses two pairs of twisted copper wire, HDSL transceivers, and multiplexers and demultiplexers at each end of a communication link to provide T1 capacity service over two pairs of twisted copper conductors commonly used in local loops within the PSTN.
In general, DSL implementations are configured such that each DSL transceiver at a CP 20 has its own dedicated interface with the customer premise equipment (CPE). In order to combine two or more DSLs at a CP 20 an additional multiplexing unit is required. The additional multiplexing unit can be realized in a programmable microprocessor or with a dedicated application specific integrated circuit (ASIC). In either case, the number of components, the complexity of the system, and the footprint of the system increases dramatically.
The prior art HDSL link illustrated in FIG. 2 is offered by way of example to highlight the additional interface equipment required as additional transmission media are added to increase the performance of a communications link. In this regard, FIG. 2 illustrates a basic HDSL network link architecture. As illustrated in FIG. 2, a HDSL network link 40 may comprise equipment located within a CO 10′, equipment located within a CP 20′, and a HDSL 50. More specifically, the central office 10′ may comprise a plurality of trunk line interfaces 11, 13, and 15, herein labeled analog trunk card, digital trunk card, and optical trunk card respectively; a digital switch 12; and a plurality of HDSL termination units—central office (HTU-C) 42a, 42b, 42c, . . . , and 42x. As illustrated in FIG. 2, each HTU-C 42a, 42b, 42c, . . . , and 42x may be coupled via two twisted pair telephone transmission lines 30 to a dedicated HDSL termination unit—remote (HTU-R) 44c (one shown for simplicity of illustration). As also illustrated in FIG. 2, the combination of the HTU-C 42c, the two twisted pair telephone transmission lines 30, and the HTU-R 44c may comprise a HDSL 50. As further illustrated in FIG. 2, the CP 20′ may comprise a customer interface 46 and customer premise equipment 48.
It is significant to note that downstream and upstream data transmissions that are transmitted across the HDSL network link 40 of FIG. 2 must be processed at the HTU-Rs 44 and the HTU-Cs 42 in order to ensure that data transmissions are inverse multiplexed and reconstructed into their original configuration. Each of the HTU-Rs 44 and the HTU-Cs 42 may further comprise a transceiver and a mapper (both not shown). At one end of the HDSL communications network 40, a first mapper may be used to inverse multiplex or distribute a data transmission across multiple transmit media. At the opposite or receiving end of the HDSL communications network 40, a second mapper may be used to multiplex or reconstruct the original data transmission. By way of example, a downstream data transmission may be inverse multiplexed such that a portion of the data is transmitted via the HTU-C 42c across a first twisted pair telephone transmission line 30a with the remaining portion of the data transmission sent via a second twisted pair telephone transmission line 30b. After the first and second portions of the data transmission are received and reconstructed by the HTU-R 44c, the first and second portions of the original data stream may be multiplexed before being forwarded to the customer interface 46 and the CPE 48. Often the customer interface 46 is implemented with a router having a port coupled with one or more HTU-Rs 44 and or other network interface devices.
It will be appreciated that the complexity and associated increase in the hardware required to implement a multiple DSL communication system may be significant factors that may prevent the success of a multi-channel DSL communication system. In light of the expected implementation and operational cost erosion for all data delivery technologies, it is highly desirable to identify and implement communication systems with increased performance with minimal added cost and complexity.
Accordingly, there is a need for a communication system and method that can increase the range and data rate of a DSL communication link between two locations while minimizing installation and operational complexity, space requirements, and cost.